A relay may be a technique of expanding a cell coverage of a mobile/wireless communication network, or improving an effective throughput. Also, the relay may configure a backhaul in a wireless manner to reduce initial investment and operation costs.
A mobile/wireless communication system using the relay may basically need six types of wireless links. As the six types of wireless links, a wireless link (eNB-R) transmitting data from a base station to the relay, a wireless link (eNB-UE) transmitting data from the base station to a terminal, a wireless link (R-eNB) transmitting data from the relay to the base station, a wireless link (R-UE) transmitting from the relay to the terminal, a wireless link (UE-eNB) transmitting data from the terminal to the base station, and a wireless link (UE-R) transmitting data from the terminal to the relay may be used.
In a current Third Generation Partnership Project Long Term Evolution (3GPP LTE) Rel-8 system, a cell-specific reference signal (RS) may need to be transmitted to all subframes of a downlink. By using the cell-specific RS, an LTE Rel-8 terminal may measure a Channel Quality Indicator (CQI) to report the measured CQI to the base station. Also, the LTE Rel-8 terminal may perform a channel estimation using the cell-specific RS so as to demodulate data.
An LTE Rel-8 frame structure may have a problem in operations of the LTE Rel-8 terminal when the relay provides services to the LTE Rel-8 terminal. Without considering the relay, an existing LTE Rel-8 terminal (legacy UE) may determine that the cell-specific RS is present in all frames. However, in a wireless link (eNB-R) interval transmitting data from the base station to the relay, the relay may need to receive data from the base station, and thereby may not transmit a signal. In this manner, when the relay does not transmit the cell-specific RS in a specific subframe, terminals provided with services from the relay may have a problem in that the terminal fails to recognize the base station.
Accordingly, in the wireless link (eNB-R) interval transmitting data from the base station to the relay, the terminal may determine a wireless link quality of the relay, providing services to the terminal, to be not satisfactory, even though the wireless link quality is superior. The terminal may request to perform an unnecessary handover to another cell, and a CQI value of a wireless channel being reported from the terminal to the relay may be inaccurate. Also, the channel estimation may be significantly inaccurately performed, and thereby a demodulation error of data may be significantly increased.